Fire detection and suppression systems that are capable of responding to the presence of either a flame or an explosion for generating an output control signal used for the activation of a fire suppressant are generally known. In military applications it is often desireable to discriminate between the thermal energy generated by a hydrocarbon fire resulting from, for example, the explosion of a fuel tank in a vehicle such as an armored personal carrier or a tank and the thermal energy generated by a "High Energy Anti-Tank" (HEAT) round. HEAT rounds can cause momentary high-energy radiation levels and high temperatures which may exceed 5000.degree. K. Such a high energy output may be due not only to the ammunition round itself but also due to a secondary reaction with the vehicle's armor. This secondary reaction has been theorized as a pyrophoric reaction. HEAT rounds may or may not, however, set off a hydrocarbon fire, depending upon whether or not the round penetrates a fuel cell and ignites the fuel therein. Thus, it is desireable to prevent the activation of a fire suppressant system when a HEAT round penetrates the armor plate of a vehicle but does not explode the fuel tank and hence, does not initiate a secondary hydrocarbon fire.
U.S. Pat. No. 3,825,754 issued July 23, 1974 to Cinzori discloses a detecting system which includes sensing means for specifically detecting a HEAT round and responding to the detection of such a round to deactivate a hydrocarbon fire detecting means for a period of time. Although well suited for many applications, this system requires external coding for various armor types. This system also requires preset primary and secondary threshold levels, does not take into consideration the thickness of the armor upon the vehicle within which the system is incorporated, does not make an allowance for the size or energy of an entering round and, the dynamic range of the round detector is generally not sufficient to measure the high intensity peaks associated with some HEAT rounds. This inability to measure some high intensity peaks may result in the detecting circuit becoming saturated by the high energy associated with the round and, thus, require that the fire sensor system be disabled for some interval of time before the circuit is enabled to detect the presence of a secondary fire.
U.S. Pat. No. 4,101,767 issued on July 18, 1978 to Lennington teaches a discrimination fire sensor which includes detecting means which discriminate between hydrocarbon fires and high-energy exploding rounds of ammunition that do not cause a hydrocarbon fire. The disadvantages inherent in this system are several. For example, the system will not readily discriminate on low energy rounds with a color temperature below 2400.degree. K. and the system will not readily discriminate if a round has penetrated a greater thickness of armor which results in the round having a color temperature of less than 2400.degree. K. Also, the dynamic range of the round detector is insufficient to measure the high intensity associated with many rounds which further results in the saturation of the circuit and thus requires that the sensor system be disabled for several milliseconds before the circuit can detect a secondary fire.